net: mscc: ocelot: Fix crash when adding interface under a lag

[ Upstream commit 34f3ff5 ]

Commit 15faa1f ("lan966x: Fix crash when adding interface under a lag")
fixed a similar issue in the lan966x driver caused by a NULL pointer dereference.
The ocelot_set_aggr_pgids() function in the ocelot driver has similar logic
and is susceptible to the same crash.

This issue specifically affects the ocelot_vsc7514.c frontend, which leaves
unused ports as NULL pointers. The felix_vsc9959.c frontend is unaffected as
it uses the DSA framework which registers all ports.

Fix this by checking if the port pointer is valid before accessing it.

Fixes: 528d3f1 ("net: mscc: ocelot: drop the use of the "lags" array")
Signed-off-by: Jerry Wu <w.7erry@foxmail.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/tencent_75EF812B305E26B0869C673DD1160866C90A@qq.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Jerry Wu

drivers/net/ethernet/mscc/ocelot.c

@@ -2307,14 +2307,16 @@ static void ocelot_set_aggr_pgids(struct ocelot *ocelot)
 
 	/* Now, set PGIDs for each active LAG */
 	for (lag = 0; lag < ocelot->num_phys_ports; lag++) {
-		struct net_device *bond = ocelot->ports[lag]->bond;
+		struct ocelot_port *ocelot_port = ocelot->ports[lag];
 		int num_active_ports = 0;
+		struct net_device *bond;
 		unsigned long bond_mask;
 		u8 aggr_idx[16];
 
-		if (!bond || (visited & BIT(lag)))
+		if (!ocelot_port || !ocelot_port->bond || (visited & BIT(lag)))
 			continue;
 
+		bond = ocelot_port->bond;
 		bond_mask = ocelot_get_bond_mask(ocelot, bond);
 
 		for_each_set_bit(port, &bond_mask, ocelot->num_phys_ports) {